I am the author of the disktuna tool, it can not recover the files, it merely tries to make files playable/viewable by appending a valid header and make header point to valid data, bypassing the the first 150 or so encrypted KB.
Your own STOP DJVU FAQ mentions my tool:
"Are there any ways to recover/repair files that can't be decrypted? In most cases this is not possible, however there is a tool that can help repair some videos that have been encrypted. This tool was made by a third-party, and they are not affiliated with us, however one of our developers has verified that it do